1. Field of the Invention
This invention relates to devices for hydraulically expanding a conduit surrounded by a structure in order to bring the conduit into contact with, or engagement with, the surrounding structure. It finds particular application in reducing the clearance between heat exchange tubes and baffle plates in nuclear steam generators, and in joining reinforcing sleeves on the inside walls of these tubes by producing interference joints therebetween.
2. Description of the Prior Art
Devices for hydraulically expanding plastically-deformable conduits are known in the prior art. Such devices generally comprise a hydraulic expansion unit, and a fluid mandrel connected thereto which is capable of applying enough hydraulic pressure to the inside of an axial section of the conduit to plastically deform the conduit. Such hydraulic expansion devices are frequently used to effect repairs or maintenance on the heat exchanger tubes of a nuclear steam generator. In such generators, it is generally difficult to gain access to the outside tube surfaces due to the density in which they are arranged, and the limited access space afforded by the few water inlets and outlets in the walls of these generators. Therefore, the most convenient way to gain access to these tubes is through their inlet ports which are present in the tubesheet dividing the primary and secondary sides of the steam generator. When the walls of these tubes have been weakened or pitted by corrosion or excessive heat and fluid currents, such hydraulic expansion devices are frequently used to join cylindrical sleeves to the insides of these tubes. When such devices are used for sleeving, a cylindrical reinforcing sleeve is first frictionally engaged over the head of the fluid mandrel. Next, the mandrel and sleeve are inserted into the mouth of the tube to the repaired. The mandrel and sleeve are then positioned along the axial section of the tube in need of repair. The hydraulic expansion unit is actuated, and the mandrel head applies sufficient hydraulic pressure to both the sleeve and the surrounding tube to plastically expand both, thereby creating an interference joint therebetween. The end result is that the hydraulic expansion device joins a sleeve across the corroded or pitted portion of the tube which reinforces the tube and shunts the flow of water away from the weakened walls of the tube and through the walls of the sleeve. Apart from a sleeving operation, such a device could also be used to effect an expansion directly on a heat exchanger tube incident to other maintenance processes.
Unfortunately, such prior art hydraulic expansion devices are not without shortcomings. For example, such devices do not consider the specific elastic and plastic properties of the tubes and sleeves being expanded. Instead, these devices attempt to create interference fittings for other expansions on the basis of a pre-selected "average" of the elastic and plastic properties of the tubes and sleeves being expanded. Hence, it is difficult to obtain truly uniform expansions with these devices. Since mechanical reliability is of paramount importance in a nuclear steam generator, such non-uniformity, and the uncertainty of results which attends it, is undesirable.
Clearly, a need exists for a hydraulic expansion device which is capable of producing highly uniform expansions in order to maximize the mechanical reliability of the system as a whole. Ideally, such a device should take into account the specific plastic and elastic properties of the tubes being expanded in determining a final swaging pressure so that a near-perfect expansion is possible in each tube.